Young girls from the countryside are also sent to the city to work as domestic helpers.

The money they earn is a lifeline for their families.

From September to December, many rural schools are closed by local officials so that tens of thousands of young children in Uzbekistan, Turkmenistan and Tajikistan can be sent into the cotton fields to bring in the harvest.

In October last year, a minister with Uzbekistan's public education department admitted that at least 44,000 senior pupils and students had been mobilised to help pick the country's cotton.

Local rights activists say the figure does not take into account the number of young children forced into the fields - they say they have seen children as young as seven working there.

"If you go to the cotton fields, the only people working are women and children," said regional analyst Michael Hall from the International Crisis Group.

Children from the ages of 10 upwards help adults to pick cotton by hand for between two and five US cents a kilogramme. A small child might be able to pick 30kg a day.

Often, employers deduct food and housing costs from what they earn, leaving them with very little. A BBC reporter who visited an Uzbek cotton field met a 12-year-old boy who said he was paid in kindling.

'White gold'

The three countries' economies are agrarian and rely heavily on the cotton industry.

Some schools are emptied for months on end

Uzbekistan's exports last year were thought to be worth at least $1bn - it is the country's most important cash crop, known as "white gold". In some parts of the country, cotton is a virtual monoculture.

Most governments in the region have signed at least one of the ILO's two conventions banning the use of child labour. Uzbekistan has not, but has legislation banning children under 15 from working.

All three governments deny accusations that children are forced into work, saying it is the parents from rural communities who send their children into the fields to earn much-needed cash.

A spokesman for the Uzbek embassy in Britain said: "There is no child labour in Uzbekistan."

But less guarded officials will say they empty out local schools because they lack machinery and have no viable alternative to bring in the harvest.

"Very often, the children come from poor rural areas where there are no opportunities to earn cash, so the children are taken out of schools to work for money," he said.

Young teenagers working as manual labour in cities may be their family's only means of support, he added.

He also believes the pressure to meet production quotas is partly to blame and that land reforms are overdue.

"Each region has state quotas on cotton that come from above. As long as these are in place, and as long as local, appointed administrators feel their survival depends on meeting them, this will continue," Mr Hall says.

The ICG is trying to get support from the international community put pressure on governments to abide by the ILO conventions and implement the law.

It also wants to raise awareness among consumers that the cotton picked by forced child labour is winding up on clothing racks in the west.

Besides the severe implications for children's education, Mr Hall said the use of forced labour has long-term consequences for political and economic stability in the region.

"This is part of a bigger picture, where rural communities are being pushed to the brink," he says, through lack of opportunities for work for a fair wage.